Clutch linings are used for friction clutches in motor vehicles, where they are riveted on either a metallic clutch plate or clutch disc, so that, in connection with a counterpart element, in the connected state, power is transmitted from an engine to a transmission unit or disconnected when the clutch is open.
At the same time, high demands are put on clutch linings since they are expected to fulfill several functions that are not easily achievable in a specific manner. A clutch lining should feature a high bursting speed in order for it not to be destroyed by centrifugal forces; it should have a high coefficient of friction with which a large torque can be transmitted, and at the same time, it must be resistant to both anti-wear and deformation under thermal and/or power influences. Nevertheless, clutch linings should be as simple as possible and thus economically viable for production.
To increase the bursting strength, and thus the clutch lining strength in circumferential direction, it is already prior art to lay impregnated extruded material with binder in wavy circumferential direction, in several shallow layers. Coils of the extruded material feature radial, inner and outer reversal areas that lie on concentric circles (German Patent DE 44 20 291 B4). The reversal areas of the coils can be distributed on several concentric circles with different diameters respectively. The radii of the circles differ sufficiently in order to prevent thickened spots along the edges of clutch lining or lining body that can lead to pressure damages on the extruded material. By this means, the proportion of the extruded material can be increased in the overall composition of the lining body material.
It is already known to configure clutch linings or friction clutch linings in two layers that comprise a base member or a reinforcement member and a facing member or a friction member to absorb bursting forces on the base member. The base member is preferably reinforced, whilst the other member (possibly non-reinforced) preferably provides the desired frictional properties (German Patent DE 44 14 058 A1, U.S. Pat. No. 5,601,174). The facing member of the friction lining simultaneously forms an abrasive layer whilst the base member essentially exercises a supporting or holding function, for which it should be rigid. However, the top layer is not optimized against deformation.
In a different, double-layered friction lining that includes a friction member and a reinforcement member, the proportion by volume between glass fibers and polyamide fibers in the friction member differs from the proportion by volume of different fibers in the reinforcement member (U.S. Pat. No. 4,244,944). Warpage or deformation of the friction lining can occur as result of this, owing to different expansion coefficients of glass and polyamide fibers.
To solve the aforementioned problems, a double-layered clutch lining from a compression-molded resin friction member is already known. This forms a friction surface and a reinforcement member in which the compression-molded friction member essentially comprises a matrix that consists of glass fibers and aromatic polyamide fibers, and furthermore consists of inorganic filler, a solid lubricant and binder resin (German Patent DE 38 04 898 C2). The reinforcement member essentially features a matrix that is selected from glass strand or glass yarn. And at least strand or yarn that is selected from a group comprising a synthetic strand or glass yarn and aromatic polyamide strand or glass yarn, wherein a binder adheres to the matrix and the strand or yarns are formed in a spiral shape. The aforementioned strand or yarns depict strands of the so-called endless fibers or filaments with corresponding length. The strength of double-layered clutch lining should be raised by the reinforcement member wound in a spiral-shape. A friction surface with a heat-resistant protective layer should be achieved with the glass fibers contained in the composition of the matrix of the compression-molded friction member. The strength of glass fiber can certainly reduce significantly when the operating temperature of the clutch lining attains the softening temperature, the reason why this does not show very good anti-wear characteristics.
In order to provide a similar, known multilayered clutch lining having improved friction and anti-wear characteristics at high temperature, the compression-molded friction member should essentially comprise a matrix with certain volume fraction of glass fiber. It further comprises at least one type of heat-resistant organic fibers from a group that comprises polyamide fibers, aromatic polyamide fibers and polybenzimidazole fibers. Furthermore it comprises at least one type of heat-resistant inorganic fibers from one group that comprises potassium titanate fibers, ceramic fibers, quartz fibers and glass-type silicon dioxide fibers; it should furthermore consist of inorganic filler, a solid lubricant and binder resin (German Patent DE 40 18 671 C2). The corresponding reinforcement member should essentially be a matrix comprising glass strand or glass yarn and heat resistant organic strand or yarn, and binder comprising resin and unvulcanized rubber that adhere to the matrix, wherein the matrix is formed in a spirally wound shape.